A signal is a function that conveys information. Values of the abscissa of the function may change continuously or at discrete intervals. Likewise, values of the ordinate of the function may change continuously (analog) or at discrete intervals (digital). An image is a signal that conveys information in two dimensions. A digital image conveys information in two dimensions at discrete intervals through an array of picture elements, or pixels.
Mathematical operations may be used to process signals. In the case of a digital image, the discrete values of a function may be arranged in a matrix so that mathematical operations are performed with respect to the elements in the matrix. Mathematical operations may be used to process a digital image for a variety of reasons. For example, a convolution operation may be used for computer vision, statistics, and probability, and for image and signal processing for noise removal, feature enhancement, detail restoration, and for other purposes. A cross-correlation operation may be used, for example, to compare the digital image with a template.